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Finding the Age of Yellowstone's Geysers and Hot Springs

January 13, 2016

USGS scientists often determine the age of volcanic rocks with dating techniques that involve radioactive decay of elements like uranium and argon.

Silica sinter (an amorphous form of silicon dioxide) forms from the...
Silica sinter (an amorphous form of silicon dioxide) forms from the waters that flow from hot springs near Shoshone Lake, Yellowstone National Park. USGS photograph by Jake Lowenstern.

Other times, for young rocks, we use carbon-14 methods. Most typically, this is done when we find trees (often converted to charcoal) buried by lava or ash, which provide an age just before eruption and burial. Recently, USGS scientists used carbon dating for a novel purpose…to date the formation time for hot springs and geysers.

At Yellowstone, most hot spring waters in the caldera are saturated with amorphous silicon dioxide, which is deposited as a material called "silica sinter"(Figure). Over time, new silica growth covers the old, resulting in layers of thick hard deposits. Anything growing or falling on the silica will be trapped as new layers are deposited. That can include bits of charcoal from forest fires, pollen falling from trees and plants, or even the thin films of thermophile lifeforms that live in and adjacent to hot springs.

Scientists Jake Lowenstern and Shaul Hurwitz took samples from shallow cores collected in the 1960s and dissolved the silica, leaving behind the organic carbon. Their colleague Jack McGeehin dated the carbon at the Lawrence Livermore National Laborary. The results were published in a January, 2016 issue of the Journal of Volcanology and Geothermal Research. The authors found that the technique is successful in silica samples as small as 15-25 grams (the weight of a double A battery). Initial results seem to indicate that the area near Old Faithful (the Upper Geyser Basin) has seen continual hydrothermal activity over the past ten thousand years.

Yellowstone sinter research article graphic representing sample col...
Graphical abstract of the new research paper. The scientists collect samples from the rocks forming near hot springs and geysers. They dissolve small amounts of the rock in acid and organic carbon (created by living organisms) remains behind. The ratio of 14-Carbon to 12-Carbon reflects how long it has been since the organisms were living (and took in 14-Carbon from the atmosphere). This provides an age estimate of the growing sinter deposit.
Secondary electron image of carbon-bearing sinter from Yellowstone ...
Secondary electron image of carbon-bearing sinter from Yellowstone hot spring; unidentified filaments of thermophilic (heat-loving) organisms with silica spherules that precipitate out of hot water.